The present invention relates to a charge coupled device (CCD) image sensor, and more particularly to a charge coupled device image sensor which can prevent smear and improve sensitivity.
Referring to FIG. 1A, first and second p.sup.- -type wells 12 and 13 are formed on a n-type substrate 11. An n.sup.+ -type photo diode 14 and an n.sup.+ -type VCCD (vertical charge coupled device) 17 which is a charge transfer area are formed in first and second p.sup.- -type wells 12 and 13, respectively. On the upper surface of n.sup.+ -type photo diode 14, a p.sup.++ -type surface isolation substrate 15 is formed and a third p.sup.- -type well 16 encompassing n.sup.+ -type VCCD 17 is formed.
A gate insulation film 19 is formed on the whole surface of the substrate. A transfer gate 20, an in-between insulation film 21 and a light-shading film 22 are sequentially formed on gate insulation film 19, except on photo diode 14. A passivation layer 23 is formed on gate insulation film 19 and the sequentially deposited gate and films.
A leveling substrate 24 is formed on passivation layer 23 and a micro lens 25 is formed on leveling substrate 24 which is on the upper side of photo diode 14.
A reference numeral 18 is a channel stop area for isolating pixels.
In a conventional charge coupled device image sensor having the above configuration, incident light through a camera lens is concentrated by micro lens 25 to be input to photo diode 14. The incident light to photo diode 14 is photoelectrically converted into charges. The photoelectrically converted charges are vertically transferred to HCCD (horizontal charge coupled device, not shown) through VCCD 17 according to a VCCD clock signal. The charges transferred to the HCCD are horizontally transferred by a HCCD clock signal. After being detected as voltage by floating diffusion at the tip of the device, the charges are amplified by an amplifier and transferred to a peripheral circuit.
In a conventional charge coupled device image sensor, light-shading film 22 is formed to shade light on the substrate, except on the photo diode 14 so that the light concentrated through micro lens 25 is input only onto the photo diode 14. As shown in FIG. 1A, light-shading film 22 is formed on both edge parts of photo diode 14. Accordingly, the light input to the edge parts of the photo diode is cut off and are not input to the photo diode by the light-shading film. So, it becomes a problem that the light-sensitivity of the photo diode decreases due to the reduced light-receiving area of the photo diode.
As shown in FIG. 1B, the concentrated light through the center portion of the micro lens 25 is input to the photo diode 14 to generate signal charges. However, it is a problem that the light input through the both edge parts of the micro lens is not input to the photo diode 14 but to VCCD 17 so as to cause smear phenomenon. In addition, one micro lens is arranged to correspond with one photo diode in fabricating the above charge coupled device image sensor. However, as a pattern size becomes smaller according to high integration, it is difficult to form the micro lens precisely corresponding to each photo diode.